The Homeland Security Department would not immediately say Wednesday whether the increased measures were in response to intelligence about a specific threat. But a U.S. counterterrorism official says American intelligence has seen indications that certain terrorist groups in Yemen and Syria are working on a bomb that could make it through airport security undetected. The official spoke on condition of anonymity because the official was not authorized to discuss the matter publicly by name.

Johnson says the U.S. is sharing recent and relevant information with foreign allies. He says the government is also consulting with the aviation industry.